I like the idea of modifying dodge in two ways. 1) You declare that the character is being attacked and if they so choose they can dodge at that point. I would say if the person has already hit it is too late. 2) Instead of a successful dodge completely negating the damage for a ranged attack, make it so that each degree of success increases the difficulty of the shot fired. They are a harder target to hit. If you are using both of these rules and do not want your players to die or do not have any other rules for adding to their survivability, I would recommend making each degree of success modify the shooting difficulty by two degrees.

Also, as far as the surprise round and rapid reaction, I have always made it so that the people with RR get to roll their initiative as normal and the sneak attacker just gets placed at the top of the order for that round, unless the players made a successful awareness test to catch a glimpse of sun reflecting off the scope or see an unusual shadow or hear a rustle or brick being knocked out of place by the attacker. If they did not pass that awareness test, why should they get to dodge the shot? And if they can't see the person to shoot at them, why should they get to dodge the shots?